1. Technical Field
The present invention relates to an actuator, an optical scanner, and an image forming apparatus.
2. Related Art
An actuator using a torsional oscillator has been known (see JP-A-2010-79243, for example).
For example, JP-A-2010-79243 discloses an optical deflector including a movable plate (movable portion), a support frame (support portion), and a pair of elastic support portions (connecting portions) that torsionally and pivotally (swingably) support the movable plate relative to the support frame, and each of the elastic support portions is formed of two bars (beam members).
The movable plate, the support frame, and the pair of elastic support portions are formed integrally with each other by anisotropically etching a silicon substrate having silicon (100) principal surfaces.
Further, in the optical deflector according to JP-A-2010-79243, the movable plate has an octagonal shape in a plan view. The movable plate having an octagonal shape in a plan view is advantageous in that the weight of portions of the movable plate that are apart from a pivotal (swing) axis and hence the moment of inertia are reduced.
The movable plate having an octagonal shape in a plan view is, however, problematic in that the shape is difficult to manufacture. In particular, when a movable plate of this type is manufactured by using anisotropic etching as described above, the combination of anisotropic etching and the crystal surface of the movable plate makes it difficult to control the shape of the movable plate, disadvantageously resulting in large variation in the shape.